A honeycomb structure is frequently used as a trapping filter for exhaust gas for environmental improvements, pollution control, and the like. Above all, there are large expectations on a honeycomb structure used in a state of being incorporated into an exhaust gas system or the like of a diesel engine as a diesel particulate filter (DPF) in order to trap and remove particulate matter contained in exhaust gas from a diesel engine or the like. As a material for the honeycomb structure, silicon carbide (SiC) is being spotlighted and used in view of having a merit of excellent thermal resistance.
However, the honeycomb structure used as a DPF has a problem of easily generating defects such as a crack due to thermal stress because temperature rise is prone to be uneven when particulate matter is trapped and removed (upon use) and when particulate matter accumulating inside the filter is combusted and removed in order to remove increase in pressure loss by particulate matter accumulating with time in the filter. In addition, since a silicon carbide honeycomb structure also has a demerit of inferiority in thermal shock resistance because of high thermal expansion coefficient to a cordierite honeycomb structure, the silicon carbide honeycomb structure has a problem of difficulty in sufficiently taking advantage of the aforementioned merit. Further, according to remarkable increase in thermal stress generated upon use and upon regeneration with respect to a conventional honeycomb filter as the filter (DPF) grows in size, the frequency and extent of generation of defects due to thermal stress are becoming more serious.
Therefore, from the viewpoint of solving these problems, there has been proposed a honeycomb structure having a structure where a plurality of honeycomb segments are unitarily bonded at bonded faces via a bonding material layer. In such a honeycomb structure, the bonding material layer functions as a cushioning material for suppressing thermal expansion and eases up thermal stress. In addition, by employing a segment structure, a distance between a portion having high temperature and a portion having low temperature is reduced, and temperature gradient is reduced. Therefore, a honeycomb structure constituted as a honeycomb segment bonded body has an excellent property of hardly causing defects such as a crack. Incidentally, as a prior art document regarding a honeycomb structure constituted as a honeycomb segment bonded body, there is, for example, Patent Document 1.
Patent Document 1: JU-A-H2-117033